This project will develop potential PET ligands for each of the three opioid receptors (the promising compounds will be radiolabeled and evaluated further in Project 1b). Both agonists and antagonists will be synthesized. A potential ligand will also be made for the ORL-1 receptor. Secondary objectives involve further synthetic research on buprenorphine-like compounds and synthesis of compounds for the Center group for primate studies that are unavailable or prohibitively expensive.